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fxus66 kpdt 090613 aaa 

Area forecast discussion
National Weather Service Pendleton or
954 PM PST sun Dec 8 2019

Updated the aviation discussion

Update...a Dry Ridge of high pressure remains in place across
the two state area with low level clouds in the basin. Patchy fog
across the area developed into areas of dense fog and freezing
fog over the lower Columbia Basin and the foothills of the or/WA
Blue Mountains. In addition the dense fog formed east toward
Meacham that had prompted dense fog advisories across the region
through the night. Meanwhile minor changes were done to temps
that are forecast to remain at or slightly above freezing and the
present short term forecast appears on track.


Previous discussion... /issued 144 PM PST sun Dec 8 2019/

Short term...tonight through Wednesday...upper trough is exiting
the region this afternoon and an upper level ridge is building in
behind it. The ridge will be the main weather feature through the
day on Tuesday. This will result in a continuation of stratus and
fog in the lower valleys. Have issued a dense fog advisory for
the Columbia Basin and adjacent foothills and valleys for tonight
and early Monday. The fog may become even more widespread Monday
night and Tuesday with the ridge overhead. Away from the fog
conditions will be fair with mild temperatures and just a few
clouds. By Tuesday evening a weak frontal band will cross the
Cascades for a chance of showers and mountain snow showers.
However quantitative precipitation forecast amounts will be rather light Tuesday night. By late
Wednesday the next much stronger system may reach the Cascade east
slopes near the very end of the day for a chance of rain and
mountain snow. The fog could linger in the Columbia Basin into
Wednesday. 78

Long term...Wednesday night through Sunday...models in good
agreement on an active pattern beginning Wednesday and continuing
into the first half of next weekend. A wet storm system looks to
impact the region Wednesday night through Friday, bringing
widespread rain and mountain snow to the forecast area. Behind
this system, a persistent moist, westerly flow will lead to
continued chances for scattered precipitation through at least
Saturday afternoon. Initially, snow levels for thursday's system
will range between 4000-6000 feet, gradually lowering to 500-1000
feet by Sunday morning. Ensembles showing the potential for quantitative precipitation forecast
ranging between 0.50-1.50" through the weekend for the higher
elevations, and ~0.30" possible on average for the Columbia Basin.
As snow levels lower, may need to consider winter weather
highlights, especially for the Cascades as well as higher terrain
of central and northeast Oregon. A weak upper level ridge begins
to move onshore by next Sunday, bringing a brief break from the
active weather. With a Pacific flow, temperatures expected to
remain near normal through next weekend with highs in the 40s and
lows in the 20s/30s. Richards

Aviation...areas of IFR and MVFR conditions can be expected at taf
sites kalw...kpdt...kpsc...kykm through most of the period.
Elsewhere MVFR conditions can be expected with some improvement to
mostly VFR conditions at taf sites krdm and kbdn after 18z.

PDT watches/warnings/advisories...
or...dense fog advisory from 7 PM this evening to noon PST Monday for

Washington...dense fog advisory from 7 PM this evening to noon PST Monday for



Preliminary point temps/pops...
PDT 31 39 29 38 / 0 0 0 0
alw 34 38 32 38 / 0 0 0 0
psc 33 37 31 37 / 0 0 0 0
ykm 28 38 28 36 / 0 0 0 10
hri 31 39 31 38 / 0 0 0 0
eln 27 37 26 35 / 0 0 0 10
rdm 26 46 24 46 / 0 0 0 20
lgd 30 42 28 41 / 0 0 0 0
gcd 28 43 26 45 / 0 0 0 10
dls 34 41 34 40 / 0 0 0 20


PDT watches/warnings/advisories...
or...dense fog advisory until noon PST Monday for orz044-502-507.

Washington...dense fog advisory until noon PST Monday for waz026>029.

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